(1) Field of the Invention
The present invention relates to a novel method for preparing solid p-disodium hydroxybenzoate.
(2) Description of the Prior Art
p-Hydroxybenzoic acid, which can be prepared by subjecting p-disodium hydroxybenzoate to a desodium process, has been industrially used in various fields as a raw material for polyesters, oligomer liquid crystals, medicines, sterilizers and the like.
Heretofore, p-hydroxybenzoic acid has been manufactured on an industrial scale mainly from phenol potassium and carbonic acid gas in accordance with the Kolbe-Schmitt reaction.
In this method, a yield of p-hydroxybenzoic acid is as low as about 60% at present, because of the poor recovery of potassium salts and because of the secondary production of phenol, salicylic acid and 4-hydroxyisophthalic acid.
Further, there is another method in which the Reimer-Tiemann reaction is performed by the use of phenol, carbon tetrachloride and sodium hydroxide in the presence of a copper powder (Organic Reactions, 28, p. 15, 1982), and in regard to this method, a higher yield can be expected. However, such a method as is satisfactory from an industrial and economical viewpoints has not been suggested yet. In the aforesaid method utilizing the Riemer-Tiemann reaction, a mixed phase regarding the reaction is remarkably non-uniformed. In this reaction system, there exist together various and intricate liquid and solid phases, for example, an aqueous phase, an organic oil phase, a catalyst powder and a crystal such as sodium chloride which is formed during the progress of the reaction. In addition, it is necessary to inhibit the secondary production of o-hydroxybenzoic acid. For these reasons, it is not always fair to say that the above mentioned Reimer-Tiemann method is industrially suitable for the manufacture of the solid p-hydroxybenzoic acid. With regard to the preparation of p-hydroxybenzoic acid, yield and selectivity have not been improved, and the process has not been simplified so far.